This invention relates to reduced and ambient temperature curable paint compositions containing amino cross-linking agents and particularly to such compositions containing fully alkylated, low imino aminoplast cross-linking agents.
Changing market preferences and increasing manufacturing concerns have inspired the automotive refinish industry to seek alternative coatings curing chemistries to isocyanate based coatings for reduced and ambient temperature curing systems.
Thermoplastic coating systems are well established for reduced and ambient temperature applications. However these coatings, typically high molecular weight polymers which form films through solvent evaporation, usually require additional processing to achieve the desired appearance, for example, in topcoats, and/or lack the desired physical properties, such as chemical resistance or exterior durability. In comparison, thermosetting coating systems, typically lower molecular weight polymers that build molecular weight during film formation through cross-linking of polymer chains, generally require less processing after application and are superior in physical properties relative to thermoplastic coating systems.
A number of isocyanate-free, reduced and ambient temperature curing, thermosetting coating systems are well established, however, these systems are usually lacking in some aspect of coatings performance, such as: speed of coating cure at reduced temperatures; humidity of chemical resistance; initial color or color change upon exterior exposure, a property important in topcoats; substrate adhesion; etc.
This invention relates to a curable coating compositions containing a film forming polymer cure with an aminoplast cross-linking agent and particularly to such compositions containing a fully alkylated aminoplast of a low imino content.
Often, known coating systems based on conventional thermosetting aminoplast resins require elevated temperatures of at least 82 C. for adequate curing. It would be desirable to provide a coating method in which relatively low temperatures, for example, below about 71 C. and preferably ambient temperatures, could be utilized. Previous attempts to develop such coating systems resulted in systems which had the disadvantages of being too time consuming and/or energy intensive or resulted in cured films which were deficient in various combinations of physical properties.
In accordance with the present invention, a coating composition and coating system have been developed which provides a superior rate of cure at reduced temperatures and results in coated products in which the films exhibit an excellent combination of properties for an intended application.